Here are the periods for the several styles of the wall paintings-
Romanesque 1100-1250
Transitional or Early Gothic, 1250-1350
High Gothic, 1350-1400
Late Gothic, 1400-1525
Renaissance, 1525-1600
Of course these dates are not exact, and some overlap is found.
While the greater number of the wall paintings were painted by unknown artists, there were a number of workshops. Most of the workshops were named after the church in which their work was first found.
Morten Maler, Morten the Painter, painted mostly in the Northwest corner of Zealand. c.1400.
The Kongsted Workshop worked in Southern Zealand. c. 1430.
The Union Workshop was named after the fact that worked both in Southern Sweden and in Northwest Zealand. c.1425.
The Isefjord Workshop worked around the Isefjord in Northwest Zealand. c. 1450.
The Three Kings Workshop worked in Zealand. c. 1640.
The Elmelunde Workshop worked in Southern Zealand and the islands south of Zealand. c. 1480
The Brarup Workshop worked in North Zealand. c. 1500.
The Traeskomaleren (the wodden shoe painters) painted on Fyn and Langeland. c. 1480.
Peter L. . . ykt painted in South Jutland. c. 1525.
This collection of slides was planned as a research tool. The earlier editions of Saxtorph's book on the Danish church wall paintings divided the churches into three groups. First the "must see" group, second, the "well worth a detour to see" group, and the rest. This collection consists of all the wall paintings in the first two groups from over two hundred churches. There have less than ten churches with wall paintings reported since this collection was made.
As the collector, I made no judgmental calls, if Santorph said the church was important, the paintings were photographed. This resulted in a number of wall paintings which are difficult to interpret.
Fortunately, since the medieval artist was limited to pigments derived from minerals. This precludes the question of "fading". The only way that the color could change would be by abrasion or being covered by dust or carbon from candles or fires. In one church, Vesteroe on Laesoe, there had been an oil burner fire, and the paintings were covered with soot. The congregation started to clean the paintings but found that the entire surface was so soft that they were erasing the images. They stopped at once, and are awaiting the conservationists from Copenhagen University to come and refurbish the frescos.
I used the Micrografx "Picture Publisher" program (All the good image programs such as Adobe, have the same features.) to enhance my slides. Fortunately, the wall paintings were all painted on plaster, and plaster when new, is white. Knowing this, I could locate a part of the wall painting that was unpainted plaster. I could measure the color, and read the numerical results for red, green, and blue. In almost 90% of my slides I found that I had to add 10 units of blue to make the tested area a light gray. I then added brightness to start with a good white. Then I used a feature of "Picture Publisher" that allowed changes in color and contrast using a joy stick approach. I finished by using a "sharpening" feature. Many of the images still have color bias.
In some cases, the original slide was so poor that the subject matter could not be seen. Most of these were recovered in useable form. Some, however, gave poor final pictures. I tried to save the important iconographic information, even if some other aspects of the image had to be sacrificed.